1. Field of the Invention
The present invention relates to a disk driving apparatus and, more particularly, to a disk driving apparatus suitable for a magnetic disk.
2. Description of the Prior Art
In a disk driving apparatus of the sector servo type, a current to drive an arm which is connected to a voice coil motor is generally obtained through a V/I (voltage/current converting) amplifier after servo information of a digital signal was converted into an analog voltage by a D/A converter. The dynamic range of the servo information, that is, the maximum output current is determined from the maximum needed acceleration of the arm upon seeking and is obtained from the specification of a required seeking time. In addition, it is required that the minimum output current corresponding to one least significant bit (LSB) output of the D/A converter is equal to or less than the minimum resolution of the movement at the time of the track following servo and than the amplitude of disturbance.
As the track density increases, the minimum output current corresponding to one LSB output of the D/A converter must be further reduced. However, there is a limitation in the number of bits of the D/A converter which is used. There is a problem such that, on the contrary, if one LSB output is determined by giving importance to the track tracing performance, the maximum output current upon seeking decreases and the seeking time increases.
To solve the above problems, there is also considered a method whereby the gain of the V/I amplifier is switched in the seeking mode and the track following mode. However, in this case, there are problems such that the number of circuits increases, it is necessary to adjust an analog section, and the like.